1. Field of the Invention
The present invention relates to a chip inductor and a chip inductor array which use a sintered magnetic member and also relates to a method of manufacturing the same.
2. Description of Related Art
Conventionally, there is proposed a chip inductor which is manufactured in the following manner. Namely, a kneaded material to be obtained by kneading a powdered magnetic material (or magnetic substance) and a binder is pressurized to form it into a rectangular parallelepiped or a cylindrical body and thereafter sinter it to manufacture a bar of the magnetic material. A conductor (or a conducting wire) is wound around the bar of the magnetic material to thereby mount a coil in a coiled manner. An external cover element is formed with the kneaded material of the powdered magnetic material and the binder to cover the coiled conducting wire. The semimanufactured product obtained in the above steps is sintered. External electrodes which are connected to both end portions of the coiled conducting wire are formed on external surfaces of the magnetic member by coating a conducting paste on external surfaces of the magnetic member.
The coiled conducting wire of the above-described conventional chip inductor is covered with the magnetic material. Therefore, a circular magnetic circuit is formed in a manner to enclose the coiled conducting wire, with the result that an inductance value is high and that there is little or no magnetic field to leak outside the magnetic material. It has consequently an advantage in that, even if the chip inductor is disposed in close proximity to other parts, there will be no influence on the characteristics as an inductor and therefore that a density of mounting parts on a wiring circuit board or the like can be made higher.
However, this inductor has the following disadvantages. Namely, when the external element is formed around the magnetic bar-like body around which the conducting wire is wound, the kneaded material is hard to enter the clearance between the winds of the coiled conducting wire on both ends thereof and the external surfaces of the magnetic member as well as the clearance between respective winds of the conducting wire. Therefore, when the external electrodes are formed, after sintering, by coating the conducting paste on the external surfaces of the magnetic member, the conducting paste is likely to enter the clearance between the external surfaces of the magnetic member and the winds on both ends of the coiled conducting wire. As a result, the conducting paste comes into contact with the winds of the conducting wire to thereby short-circuit a part or whole circumference of the winds of the conducting wire, resulting in a variation in the impedance characteristics. Further, the conventional method of manufacturing the inductor has, aside from the above-described disadvantage in that it is not suitable for mass production, another disadvantage in that, due to shrinkage of the kneaded material for the external cover element at the time of sintering, a pressure is applied to the internal magnetic element via the coiled conducting wire and/or via a clearance between winds of the coiled conducting wire. The magnetic characteristics are consequently badly affected and the impedance characteristics are deteriorated.
The present invention has an object of providing a chip inductor and a chip inductor array which are free from the above-described disadvantages and which are suitable for mass production and superior in, and do not fluctuate in, impedance characteristics. It has also an object of providing a method of manufacturing the same.
In order to attain the above and other objects, the present invention provides a chip inductor comprising: a coiled conducting wire; a magnetic member which is formed by sintering and in which the coiled conducting wire is embedded; wherein both end portions of the coiled conducting wire are exposed to both end surfaces of the magnetic member; external electrodes which are formed with conducting thin films and which are connected to respective end portions of the coiled conducting wire; and an inorganic material which is interposed in a clearance between winds on both end portions of the conducting wire and external surfaces of the magnetic member and a clearance between adjoining winds of the conducting wire.
The inorganic material may be wound around a winding core inside the magnetic member in a coiled manner together with the conducting wire in a side by side relationship with each other.
The conducting wire may be coated on an external surface thereof with the inorganic material and is closely wound.
Preferably, the inorganic material is a magnetic material, a dielectric material, or an electrically insulating material.
According to another aspect of the invention, there is provided a method of manufacturing a chip inductor comprising the steps, in the order mentioned, of: forming an elongated winding core by extruding a kneaded material which is obtained by kneading a powdered magnetic material and a binder; winding a conducting wire around the winding core in a coiled manner; filling an inorganic material which is free from perishing by sintering into a clearance between adjoining winds of the conducting wire by covering the winding core wound by the conducting wire with the inorganic material; forming an external cover element by extruding the kneaded material to cover the winding core and the conducting wire, the winding core and the external cover element constituting a magnetic member; sintering the winding core, the inorganic material, and the external cover element to thereby obtain a continuously formed chip inductor main body; cutting the continuously formed chip inductor main body into a predetermined length to thereby obtain a plurality of cut chip inductor main bodies, each of the cut chip inductor main bodies having the inorganic material interposed in a clearance between a wind on each end of the conducting wire and each of external surfaces of the magnetic member and a clearance between adjoining winds of the conducting wire; and forming a conducting coating on each of the external surfaces of the magnetic member of each of the cut chip inductor main bodies, the conducting coating serving as an external electrode connected to each exposed end of the conducting wire.
Preferably, the step of filling an inorganic material into a clearance is performed by extruding, by spraying, by dipping, by winding the inorganic material around the winding core in a coiled manner together with the conducting wire in a side by side relationship with each other, or by closely winding the conducting wire, which is coated on an external surface thereof with the inorganic material, in a coiled manner around the winding core.
The inorganic material may be a magnetic material, a dielectric material, or an electrically insulating material.
According to still another aspect of the invention, there is provided a chip inductor comprising: a plurality of conducting wires closely wound in a coiled manner, each being coated on an external surface thereof with an electrically insulating inorganic material which is free from perishing by sintering; a magnetic member in which the plurality of conducting wires are parallelly embedded; connecting electrodes to connect in series exposed ends of each of the conducting wires; and external electrodes which are connected to respective end portions of the connected conducting wires.
According to still another aspect of the invention, there is provided a method of manufacturing a chip inductor comprising the steps, in the order mentioned, of: forming a plurality of parallelly disposed elongated winding cores by extruding a kneaded material which is obtained by kneading a powdered magnetic material and a binder; closely winding a conducting wire in a coiled manner around each of the winding cores, the conducting wire being coated on an external surface thereof with an electrically insulating inorganic material which is free from perishing by sintering; forming an external cover element by extruding the kneaded material to continuously cover each of the winding cores and each of the coiled conducting wires, the winding cores and the external cover element constituting a magnetic member; sintering the winding cores and the external cover element to thereby obtain a continuously formed chip inductor main body; cutting the continuously formed chip inductor main body into a predetermined length to thereby obtain a plurality of cut chip inductor main bodies; and forming connecting electrodes to connect in series exposed ends of each of the conducting wires and external electrodes connected to respective end portions of the connected conducting wires.
According to still another aspect of the invention, there is provided a chip inductor array comprising: a plurality of conducting wires closely wound in a coiled manner, each being coated on an external surface thereof with an electrically insulating inorganic material which is free from perishing by sintering; a magnetic member in which the plurality of conducting wires are parallelly embedded; and external electrodes which are formed on external surfaces of the magnetic member and which are connected to both exposed ends of each of the conducting wires.
The method of manufacturing a chip inductor array comprises the steps, in the order mentioned, of: forming a plurality of parallelly disposed elongated winding cores by extruding a kneaded material which is obtained by kneading a powdered magnetic material and a binder; closely winding a conducting wire in a coiled manner around each of the winding cores, the conducting wire being coated on an external surface thereof with an electrically insulating inorganic material which is free from perishing by sintering; forming an external cover element by extruding the kneaded material to continuously cover each of the winding cores and each of the coiled conducting wires, the winding cores and the external cover element constituting a magnetic member; sintering the winding cores and the external cover element to thereby obtain a continuously formed chip inductor array main body; cutting the continuously formed chip inductor array main body into a predetermined length to thereby obtain a plurality of cut chip inductor array main bodies; and forming external electrodes which are respectively connected to exposed end portions of each of the plurality of winding cores. The external electrodes are formed on external surfaces of the magnetic member.
Preferably, a mixing ratio of the powdered magnetic material and the binder of the winding core is equal to a mixing ratio of the powdered magnetic material and the binder of the external cover element, and a particle size of the powdered magnetic material for the winding core is equal to a particle size of the powdered magnetic material for the external cover element such that a shrinkage percentage of the winding core becomes equal to a shrinkage percentage of the external cover element.
The above-described chip inductor and chip inductor array have the inorganic material in a preferred form of the magnetic material, the dielectric material, or the electrically insulating material which is interposed in a clearance between winds on both end portions of the conducting wire and external surfaces of the magnetic member and a clearance between adjoining winds of the conducting wire. Therefore, when the external electrodes and/or connecting electrodes which are made with conducting coatings are formed on external surfaces of each of the chip inductor main bodies or the chip inductor array main bodies, the conducting paste does neither enter nor contact the ends on both end portions of the conducting wire. As a result, the coiled conducting wire is not short-circuited by the conducting paste and, consequently, the impedance value does not fluctuate. In case this inorganic material is the magnetic material, the clearance between the winds of the conducting wire is filled with the magnetic material and, therefore, the impedance characteristics are improved. In case the inorganic material is the dielectric material, when the inductor is used for removing noises, the distributed capacitance between the winds becomes large and, therefore, the attenuation characteristics of the signals become steeper than the conventional one without the dielectric material layer. A chip inductor and chip inductor array which are superior in frequency selection characteristics can thus be obtained, and they can be effectively used in case where the frequencies of the signals to be transmitted and of the noises to be reduced are close to each other.
When an elongated winding core is formed by extruding a kneaded material which is obtained by kneading a powdered magnetic material and a binder, and the inorganic material is filled into the clearance preferably by winding the inorganic material around the winding core in a coiled manner together with the conducting wire in a side by side relationship with each other, and when the conducting wire which is coated on an external surface thereof with an electrically insulating inorganic material which is free from perishing by sintering, is closely wound in a coiled manner around the winding core, the winds of the conducting wire do not come into contact with each other. Therefore, as compared with the one in which the conducting wire without the coating is wound, the conducting wire can be wound more closely, with the result that the impedance characteristics can be improved and that the chip inductor and the chip inductor array can be made smaller in size.
According to the present invention, a plurality of chip inductor main bodies can be manufactured at the same time by the following steps, namely, in one aspect, a first step of forming an elongated winding core by extruding a kneaded material which is obtained by kneading a powdered material and a binder, and a second step of winding a conducting wire around the winding core in a coiled manner, and a third step of filling an inorganic material which is free from perishing by sintering in to a clearance between adjoining winds of the conducting wire by covering the winding core wound by the conducting wire with the inorganic material, preferably by means of extruding, by spraying, or by dipping, or else by winding the in organic material around the winding core in a coiled manner together with the conducting wire in a side by side relationship with each other; and in another aspect, a first step of forming a plurality of parallelly disposed elongated winding cores by extruding a kneaded material which is obtained by kneading a powdered magnetic material and a binder, and a second step of closely winding a conducting wire which is coated on an external surface thereof with an electrically insulating inorganic material which is free from perishing by sintering, in a coiled manner around each of the winding cores; and in both aspects, thereafter by the step of forming an external cover element by extruding the kneaded material to cover one or a plurality of winding cores and the conducting wires (the winding core and the external cover member constitute a magnetic member), and the step of sintering the winding core or cores, the inorganic material, and the external cover element to thereby obtain a continuously formed chip inductor main body, and the step of cutting the continuously formed chip inductor main body into a predetermined length to thereby obtain a plurality of cut chip inductor main bodies.
In manufacturing a chip inductor array of the present invention, a plurality of inductor main bodies manufactured in the method of a still another aspect of the present invention can be utilized. Preferably, a mixing ratio of the powdered magnetic material and the binder of the winding core is made equal to a mixing ratio of the powdered magnetic material and the binder of the external cover element, and a particle size of the powdered magnetic material for the winding core is made equal to a particle size of the powdered magnetic material for the external cover element so that a shrinkage percentage of the winding core becomes equal to a shrinkage percentage of the external cover element. Then, the stress due to shrinkage of the external cover element at the time of sintering is not applied to the winding core via the coiled conducting wire and/or via the clearance between adjoining winds of the conducting wire. The impedance characteristics are thus not impaired, and the impedance is improved as compared with the conventional inductor.